For correcting an abnormal curvature of the cornea of an eye, such as myopia, hyperopia and astigmatism, or for treating opacity of the cornea, it is known to surgically remove portions of the cornea by rubbing it with a spatula-like scalpel, or by grinding it with a rotating file. However, in the case of using such a spatula-like scalpel or a file, drawbacks have been encountered in that it has been difficult to accurately form the optical axis of the eye since the eyeball moves during the operation. Thus, the cornea operation could not be performed smoothly and neatly, and satisfactory results could not be expected. Further, much time has been required for the curing the cornea after the operation. Alternatively, there is already known a method of operating on the cornea using a laser knife, as disclosed for example, in U.S. Pat. No. 4,718,418 and U.S. Pat. No. 4,994,058. However, even with this lease operation method, there have been problems associated with using a laser that adversely affects the cornea. Specifically, the laser generates and intense photochemical hear, which attacks the tissue of the cornea, so that after the operation, the cornea is liable to undergo a tissue destruction, a burn, alternation, distortion, opacity and so on and much time is required for the curing after the operation.
To solve these problems, an operation on the cornea has now been conducted using an ultraviolet laser, particularly an excimer laser, which is said to curtail the effects of photochemical heat among lasers; however, even with the excimer laser, the effects due to a photochemical thermal reaction can not be entirely avoided.
When ablating the tissue of the cornea with an excimer laser, the molecules of the cornea are cut, and this is called ablation. When the excimer laser is applied to the cornea, many free radicals are produced with the ablation, and also it is thought to produce the following phenomenon occurs. The moisture in the corneal stroma is dissipated as steam upon laser beam radiation, and also is heated to a temperature of 200.about.300.degree. C. to be formed into bubbles in the cornea, and moves actively to destroy the arrangement of collagen in the corneal stroma. Further, the excimer laser beam, when impinging on the collagen, cuts the bond of the molecules thereof to produce a plume (mushroom-shaped cloud) to produce a local thermal imbalance condition, thereby generating a high temperature of 1000.degree. C. This high temperature diffuses to the neighborhood cells to impart a thermal equilibrium condition to the cornea in the vicinity of the laser beam-irradiated portion, thereby causing a temperature rise of about 15.degree. C. as a whole to impart a thermal trouble to the corneal stroma, which creates the cause of the opacity. Furthermore, when the excimer laser beam is applied to the cornea, an impact sound is produced, and a high pressure impulsively develops. As described above, even if the excimer laser is used, the temperature of the cornea rises, and the arrangement of the collagen of the cornea is destroyed, and stresses due to the pressure increase are applied to the cornea, and particularly opacity develops immediately beneath the surface layer of the cornea. Thus, these side effects can not be avoided. Also, a collagen-like material is secreted from the endothelial cells to Descemet's membrane.
It is an object of this invention to provide a method of operating the cornea of an eye by the use of an ultraviolet laser, in which the side effects caused by the photochemical thermal reaction can be suppressed as much as possible.
Another object of the invention is to provide an apparatus that can be effectively used for the above operation.